1. Field of the Invention
The invention belongs to a field of a lithium ion battery, and relates to a lithium lanthanum titanate composite solid electrolyte material containing silicon, which has high reliability, and which is used in a lithium ion battery, and a synthesizing method thereof.
2. Description of the Related Art
As the pressure for energy conservation and environmental protection increases, countries of the world have employed a strategy for development of automobile industry, and the strategy is to develop clean and high-efficient transportation means and to replace conventional vehicles, which use gasoline and light oil, with the transportation means, in order to reduce dependency on petroleum oil and to reduce environmental pollution. When developing a vehicle using new energy, higher-level requests regarding the storage of power/energy are made. A power battery needs to be smaller, lighter, and safer. A lithium ion battery is regarded as the optimum power battery to be used in a future vehicle using new energy, because the lithium ion battery has high operating voltage, high mass density, and high energy density, and thus, the lithium ion battery is superior to other secondary batteries.
In all concept cars using new energy that are currently being developed by major automobile manufacturers in the world, the lithium ion battery is used as the power battery. However, in vehicle models that are actually mass-produced, the lithium ion battery is seldom used. The advantage of this kind of electrolyte is that conductivity of the electrolyte is high. However, this kind of battery needs to be tightly sealed to ensure that the electrolyte in a liquid state does not leak. Because the battery needs to be tightly sealed, there is a limit on the decrease in the volume of the battery. In addition, because most of the electrolytes in a liquid state or a gel state are combustible organic substances, combustion may be caused in the battery under the condition that the electrolyte receives heat or a chemical reaction occurs between the electrolyte and an electrode.
However, a solid inorganic electrolyte can make up for the shortcoming of the electrolytes in the liquid state or the gel state. Therefore, persons skilled in the art are conducting research and development of the solid electrolyte on a massive scale. However, the largest barrier for practical use of the solid inorganic electrolyte is that conductivity of the solid inorganic electrolyte is extremely low, and much lower than conductivity required for commercial use (for example, conductivity reaching 10−3 S/cm).
Among many solid inorganic electrolytes that have been discovered by persons skilled in the art, a solid inorganic electrolyte whose conductivity is relatively near the level required for commercial use is a lithium lanthanum titanate (LLTO) compound. The chemical formula of LLTO is Li3xLa2/3-xTiO3 (0<x<0.16). Although the conductivity of the crystal grain thereof has already reached 10−3 S/cm, the grain boundary conductivity thereof is lower than 10−5 S/cm. This decreases the conductivity of LLTO. Therefore, LLTO does not meet the requirement for practical use. Improvement of the grain boundary conductivity is the most direct and effective method for improving the conductivity of the solid oxide conductor for lithium ions. This is a bottleneck issue when using the solid oxide electrolyte. The invention provides a lithium lanthanum titanate composite solid electrolyte material containing silicon, in which the conductivity of LLTO is effectively improved, and which is a promising material to be used in a high-efficient power lithium ion battery.